The concept of separating platinum anions from base metal cations in chloride media using native or chemically modified activated carbons has been discussed in various journals within the context of batchwise systems.
A variety of materials have been investigated for removal of metals from metallurgical effluents, ranging from inorganic materials to organic polymeric resins. Methods that have been applied to the recovery of precious metals from its solutions include zinc-dust cementation (Miller et al., 1990), carbon adsorption (Xu et al., 1995), solvent extraction (Wan and Miller, 1986; Mooiman and Miller, 1991) and ion exchange (Hubicki et al., 2006), precipitation coagulation, evaporation and membranes processes. A few authors have reported that commercial resins are unable to compete with activated carbons in terms of adsorption performance due to poor mechanical stability of the beads and inability to withstand complex elution and regeneration processes (Warshawsky et al., 2000).
Kasaini et al. 2005 developed a novel technique for recovering PGMs from dilute multi-component halide solutions using chemically modified adsorbents. However, this separation technique has not been tested on continuous fixed-bed adsorption columns. The work carried out in this study was focussed on separating platinum ion metal from base metals (iron and chromium) in fixed-bed columns containing native and chemically modified activated carbons.
Adsorption of metal ions on the surface of activated carbons takes place at the solid-liquid interface within and outside the pore structure. The charged metal ions are held strongly on the surface of activated carbons by either attractive forces (physical adsorption) or covalent bonds (chemisorption). The three major stages that accompany metal adsorption are as follows (Dinesh et al., 2005; Belgin, 2002): (a) Film diffusion, which is the transfer of adsorbate ions through the “surface film” surrounding solid particles, (b) Pore diffusion, whereby adsorbate molecules are transferred through the micropores to the adsorption sites, (c) Adhesion of the adsorbate ions to the surface of activated carbons prior to chemisorption or charge transfer complexation.